Catheterization is a medical procedure in which a long, flexible tubular catheter is advanced into and through a passage (lumen) in the human body to place an end of the catheter at a selected target site within the body. The catheter is adapted to perform a specific procedure once it has reached the target site. Many catheterization procedures involve the use of a thin, flexible guidewire which is first placed in the patient and is manipulated and advanced to the target site. Once the guidewire is in place, the physician then may advance the catheter over and along the guidewire so that the guidewire can guide the catheter to the intended site. The catheter typically is provided with a lumen that receives the guidewire.
In some catheterization procedures, it may become necessary to change catheters during the procedure. One type of procedure in which it is common to make a catheter exchange is in percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These angioplasty procedures typically involve the use of a catheter having an inflatable balloon at its distal end. The balloon is relatively inelastic and is inflatable to a predetermined size. The object of the angioplasty procedure is to widen the flow passage in the patient's artery, which may have become obstructed with a atherosclerotic plaque. In the angioplasty procedure, the physician manipulates the balloon catheter to place the balloon, while in a deflated condition, in the arterial obstruction (stenosis). Then the balloon is inflated under substantial pressure to forcibly dilate the region of the stenosis. A balloon angioplasty catheter typically has an elongate flexible shaft having a proximal end (outside the patient) and a distal end (inside the patient). A balloon is mounted to the distal end of the catheter shaft. Two lumens (passageways) extend through the catheter shaft. One lumen communicates with the interior of the balloon to inflate and deflate the balloon. The other lumen extends all the way through the catheter shaft and is open at the distal tip of the catheter shaft, beyond the balloon, such lumen serving to receive the guidewire. The guidewire lumen also can be used to measure the blood pressure in the patient's artery as well as to inject radiopaque contrast liquid into the artery so that the anatomy of the artery may be visualized under X-ray fluoroscopy. The physician may wish to remove the guidewire from the guidewire lumen while making such pressure measurements or injecting the radiopaque contrast liquid in order to have a larger fluid flow area through the lumen.
It may become necessary during the angioplasty procedure to exchange the indwelling catheter for another catheter. For example, a catheter exchange may be indicated when the balloon has dilated the stenosis to the full diameter of the balloon and when it is desired to still further dilate the stenosis with a larger diameter balloon. The indwelling catheter may be exchanged for a catheter having a larger balloon. A catheter exchange also may be indicated in those situations where the stenosis is so tight that the physician cannot advance the deflated balloon into the stenosis. Under those circumstances, the physician may wish to exchange the catheter for one having a smaller balloon, or a balloon specially constructed to have a lower profile (smaller effective diameter) when deflated.
Among the devices used to facilitate catheter exchanges is to modify the catheter to shorten the guidewire lumen so that it does not extend the full length of the catheter. A catheter having such a shortened guidewire lumen may be advanced along and be guided by the guidewire in monorail fashion. As will be appreciated by those skilled in the art, a monorail type of catheter facilitates catheter exchanges in that, because the guidewire lumen is short, it will not completely cover the exposed proximal end of the guidewire during the catheter exchange. Consequently, it is unnecessary to use long exchange wires or extendable guidewires. A significant disadvantage, however, of the monorail type of catheter is that by shortening the guidewire lumen, the catheter loses its capability to inject radiopaque contrast liquid or make pressure measurements, because the guidewire lumen does not extend fully to and is not accessible at the exposed proximal end of the catheter.
It would be desirable, therefore, to provide a monorail catheter in which the catheter also has the capability of making pressure measurements and injecting radiopaque contrast liquid.